Brushability is the ability of paint to be easily and uniformly applied to a surface using a paint brush. Brushability is adversely affected as a result of brushmarks (striations) that do not flow out, sagging, high brush drag that makes brushing difficult, and low brush drag that makes brushing so easy that overspreading of the paint occurs. Other defects such as cratering or uneven coating thickness can also occur. Lap marks will occur if the paint formulation or the way that it is being applied will not allow a wet edge to be maintained, i.e., there would be a difference in the gloss between dried layer and next abutting wet layer being brushed. Brush drag, a measure of the ease or difficulty of the brushing action, is a major factor in brushability. High brush drag helps produce high film thickness, but can make brushing so difficult that the painter can easily get tired of applying paint. Low brush drag means that the paint may be easy to apply, but then would result in an application thin uneven coating with poor hiding. The brushability of two-pack cure coating compositions, i.e., enamels, is even more difficult to achieve since it is difficult to control premature curing of a pot mix on paint bristles as well as different parts of bristles containing pot mix that have been exposed to the paint.
Moreover, another key aspect of brushable coating composition is its sag resistance. Layers of coating compositions over slanted or vertical substrate surfaces tend to sag when first applied. The thickness of the layer applied, component contents in the composition as well as its viscosity do affect the overall sagging of the applied layer. The lesser the sag, the better is the sag resistance of the applied layer. Thus, a need still exists for a brushable solvent borne ambient cure enamel that has low brush drag, low VOC, desired coating properties, such as gloss but one that also has improved sag resistance.
In the past, Kaolin has been used to improve the brushability of two pack coating compositions, such as enamels. However, the presence of Kaolin could affect the coating properties of a coating when exposed to environmental damage such as abrasion from dirt and grime on the road and cracking. Thus, a need exists to improve the brushablity of a coating composition having improved sag resistance of a layer resulting therefrom, especially for ambient cure automotive paint used in refinish applications.